Emitters

[MichalMarsalek]

This is based on #343 to prevent conflicts, that should be reviewed and merged first.

• Changes PathFragment to always be an object. "consequent" is changed to {prop: "consequent"}
• Defines a $ object for short PathFragment construction.
• Refactors emitters. Emitter transforms a Node to a string, there's no separate Detokenizer defined on the Language. Defines several abstract emitters on top of that. All languages emitters are rewritten using an emitter that uses a sort of visitor pattern approach.

I'm not 100% happy with the minPrecForNoParens method on PrecedenceVisitorEmitter, ideally, that should be abstracted away / calculated automatically.